Fish stocks

Fish stocks

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The Status of Australian fish stocks reports 2016 focuses on the status of biological fish stocks wherever possible; and, it is important to distinguish between biological stocks and fisheries. Biological stocks are relatively discrete populations of a fish species, usually in a given geographical area and with limited interbreeding with other biological stocks of the same species.

Although one fish species may exist in many geographical locations around Australia (or worldwide), fish caught in different areas may come from separate biological stocks. Individual biological stocks may be found in a single jurisdiction or may be shared across two or more jurisdictions. In some cases, individual biological stocks may also extend into the high seas. The size and distribution of individual biological stocks vary greatly between species. For example, Southern Bluefin Tuna comprises a single biological stock that spans much of the world's southern oceans. In comparison, hundreds of separate biological stocks of Blacklip Abalone are thought to exist in Australia. Because separate biological stocks have limited connectivity, fishing one may not directly affect others. Hence, it is important to assess each biological stock separately, where possible.

Biological stocks are natural resources, and different biological stocks may have different natural abundance, growth rates and mortality rates. Different biological stocks may also be influenced by different environmental factors, depending on where they occur. As a result, the amount of catch that can be sustainably removed may vary from one biological stock to another, even within a species.

In contrast, fisheries are management units engaged in harvesting fish. Fisheries are typically defined in terms of the people involved, the species caught, the area of water or seabed fished, fishing methods and the types of boats used. A single biological stock may be caught by one or a number of fisheries. Similarly, a single fishery may catch one or a number of different species, from one or more different biological stocks. Some of the species and biological stocks fished by Australian fisheries are migratory, and are taken in both the Australian EEZ and the high seas or the EEZ of other countries.

A key measure of fisheries management performance is the status of the fish stocks—the natural resource on which the fisheries depend. Therefore, the Status of Australian fish stocks reports 2016 provides status classification for fish stocks. Where possible, this takes into account the impacts of all fisheries at the level of individual biological stocks. Where the stock delineation is not known (that is, it is not known exactly where one biological stock finishes and the next begins) or the numbers of biological stocks for a species are very high, reporting has been undertaken at the level of either the jurisdiction or the management unit. The level of reporting (biological stock, management unit or jurisdiction) for each species is presented at the beginning of each chapter, along with the rationale for this choice. In these reports, the term 'stock' is used generically to refer to all three levels of stock status assessment—biological stocks, management units and populations assessed at the jurisdictional level. In future, it is hoped that most species currently assessed at the management unit or jurisdictional level will be assessed at the biological stock level, wherever research has been able to determine the biological boundaries of the stocks for the species.

See the list of the top ten sustainable fish stocks.